A liquid hydrocarbon fuel such as methanol is reformed by a reformer in order to obtain a gas containing hydrogen which is supplied to a fuel cell. The reformer uses water and fuel in a gaseous state. Consequently a vaporizer or a heat exchanger is generally provided in the fuel cell system in order to vaporize the water and the liquid fuel.
Heat required for the vaporizer or the heat exchanger is often supplied by a combustion gas from a combustor which combusts anode off-gas from the fuel cell with air or which combusts reformate gas with air. However when starting up the fuel cell system, the problem arises that either reformate gas or an anode off-gas to be combusted in the combustor can not be obtained or that the produced amount thereof is insufficient. Tokkai 2001-52730 published by the Japanese Patent Office in 2001 discloses a fuel cell system provided with a catalytic combustor which combusts a part of the liquid fuel to be introduced into the vaporizer or a different liquid fuel with air when starting up the fuel cell system. The combustion gas produced by the catalytic combustor flows into the vaporizer or the heat exchanger.